Meaning of “in” - Learner’s Dictionary

in

adverb uk us /ɪn/
INTO A SPACE

A2 into an area or space from the outside of it:

He rushed in halfway through the meeting.
Annie opened the car door and threw her luggage in.
AT A PLACE

B1 at the place where a person usually lives or works:

I called her, but she wasn't in.
Could you ask him to phone me when he gets in?
TRAIN/PLANE

B1 If a train, plane, etc is in, it has arrived at the place it was going to:

My train gets in at 17.54.
SENT

B2 given or sent to someone official in order to be read:

Applications must be in by 28th February.
TOWARDS LAND

used when the sea or a ship moves close to land:

Let's go - the tide is coming in.
be in for sth informal

If someone is in for a surprise, treat, shock, etc, it will happen to them soon:

If he thinks looking after a baby is easy, he's in for a shock.
be in on sth informal

If you are in on something, you know about it or are involved in it:

Were you in on the surprise?
Please let me in on (= tell me) the secret.
SPORT UK

In cricket and similar sports, if a person or team is in, they are taking a turn to play.

be in for it ( also UK be for it) informal

to be in trouble

(Definition of “in adverb” from the Cambridge Learner’s Dictionary © Cambridge University Press)